Wireless communications devices, such as user equipment (UEs) or base stations, communicate wireless signals through propagation of electromagnetic waves in air. Due to reflection, refraction, and diffraction along the propagation path of the electromagnetic waves, the direction of an electric field vector of the wave often varies. Each wave may be decomposed into two orthogonal components or polarizations, such as vertical and horizontal polarizations. The term “polarization” refers to the direction of the electric field. In the context of waveguides, each polarization may have several modes. Waveguide modes are typically identified as transverse electric (TE) modes with integers after them: e.g. TEm,n. The numerals M and N are always integers that can take on separate values from 0 or 1 to infinity. These indicate the wave modes within the waveguide. Only a limited number of different m, n modes can be propagated along a waveguide dependent upon the waveguide dimensions and format. In the context of rectangular waveguides, for each waveguide mode there is a definite lower frequency limit. This is known as the cut-off frequency. Below this frequency no signals can propagate along the waveguide. As a result the waveguide can be seen as a high pass filter. It is possible for many waveguide modes to propagate along a waveguide. The number of possible modes for a given size of waveguide increases with the frequency. There is only one possible mode, called the dominant mode, for the lowest frequency that can be transmitted. It is the dominant mode in the waveguide that is normally used. For rectangular waveguides, the TE10 mode of propagation is the lowest mode that is supported. Conventionally, for rectangular waveguides, the width, i.e. the widest internal dimension of the cross section, determines the lower cut-off frequency and is equal to ½ wavelength of the lower cut-off frequency. For rectangular waveguides, the TE01 mode occurs when the height equals ½ wavelength of the cut-off frequency.
Linearly polarized waves that include vertical and horizontal polarization components are commonly used in wireless communications systems. Some wireless communications devices have antennas that are only able to use a single component, typically the vertical polarization. The other component, such as horizontal polarization, cannot be received and processed at the receiver and is therefore lost.
Accordingly, the signal power represented in the unused polarization is wasted. In order to meet the signal strength required at a receiving device, transmitting devices typically increase their transmitting power to compensate for the wasted signal power at the receiving end. This in turn results in inefficient use of power at the transmitting device, and increases overall interference and noise level of the wireless communications network.
Some wireless communications devices can use two orthogonally polarized antennas that are aligned to receive two orthogonal polarizations. However, due to the size limitation, these antennas are difficult to implement in mobile devices such as handsets.
Existing microwave devices that allow handling dual-polarized signals are structurally complicated and space consuming. For example, conventional cross-polarized (X-pol) orthomode transducers (OMTs) in millimeter wave bands, such as turnstile junction OMT and Atacama Large Millimeter Array OMT, typically have a large non-planar profile and thus take up a large 3 dimensional space and are difficult to integrate into a printed circuit board (PCB).
Therefore, it is desirable to provide microwave devices that can process both orthogonal components of a polarized wave using a planar structure, and that can be effectively integrated into a PCB.